Instruction manual

FUNCTIONAL DESCRIPTION
Tie Trunk (TN760B)
The Tie Trunk Circuit Pack (Figure 3-15) interfaces four 6-wire tie trunks and the TDM bus.
Two tip and ring pairs form a 4-wire analog transmission line. An E and M pair are used for
signaling. The T and R pair transmit analog signals from the circuit pack. The T1 and R1 pair
receive analog signals from the tie trunk. The E and M pair are dc signaling leads used for
call setup handshaking. The E lead receives signals from the tie trunk and the M lead
provides signals from the circuit pack. The TN760Bs four port circuits support Type I, Type I
Compatible, or Type V signaling. Incoming and outgoing trunks can be either automatic,
immediate start, wink start, or delay dial. The Tie Trunk has the following unique circuitry:
● Ground Detector Circuit
This circuit determines if a ground has been applied to the E lead. Ground detector
inputs come from the port circuits as an analog current to the -48 volt dc supply. Its
output is a port control point to the port I/O circuit.
● Port I/O Circuit
This circuit consists of bus expanders for communication between the on-board
microprocessor and the port circuits. It receives commands from the on-board
microprocessor and distributes them to the individual port circuits. It also accesses
the port circuit scan points and passes the information to the microprocessor.
● Port Circuits
The four port circuits are identical, except for port 3 where part of the E-lead
maintenance circuit is located. Each port circuit consists of a codec with associated
input and output line transformers, analog operational amplifiers, a power filter.
loop-around transistors, port control comparators, a relay driver, an electronic power
feed device, an E-lead test maintenance circuit, and surge protection circuits.
The codec converts the incoming 4-wire analog signal from the tie trunk to a PCM
data signal. The codec converts the incoming PCM data signal from the NPE to an
analog signal. outgoing and incoming line transformers provide dc isolation to the tip
and ring leads.
Analog operational amplifiers provide amplification and buffering for
the codec and network and loop-around gain compensation. Filtered power is
provided to the codec and amplifiers.
The loop-around transistors are under control of the port control comparators and
provide a loop-around path for the signal for testing purposes. The relay driver
buffers and inverts the relay drive signals from the port I/O circuit so that a logic high
input operates the appropriate relay. The relays and electronic power feed device
control the M-lead circuitry to provide the proper signaling handshake for call
progress tones and dial pulse dialing.
The electronic feed device provides a -48 volt dc current to the M-lead circuits. It
also tests the M-lead circuits for opens or shorts and prevents uncontrolled operation
during power-up.
The E-lead test circuit provides a ground to the ground detector
circuit for testing purposes.
The surge protection circuitry provides lightnlng surge
and power cross protection for the circuit pack.
For each port circuit, E&M/Simplex
and surge protection are selected by switch settings as shown on Figure 3-16.
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